Coil components including a drum-shaped core, a winding wound around the core, and an exterior resin formed between an upper flange and a lower flange of the core have been known as coil components for use in electronic devices. For example, Japanese Patent Application Laid-Open No. 2010-16217 (Patent Document 1) discloses a coil component in which the space between an upper flange and a lower flange is filled with an exterior resin including a thermosetting resin and an inorganic filler. The coil component is characterized in that the proportion of the inorganic filler to the exterior resin is 70 to 90 mass %. In addition, the coil component is characterized in that the inorganic filler includes a spherical filler, and the proportion of the spherical filler to the exterior resin is 20 mass % or more. The spherical filler included in the inorganic filler in the proportion mentioned above retains the fluidity of the exterior resin during filling, thus improving the productivity of the coil component. In addition, the exterior resin including the inorganic filler in the proportion mentioned above can bring the linear expansion coefficient of the exterior resin closer to that of the core, thereby increasing the heat cycle resistance of the coil component.
However, the heat cycle test described in Patent Document 1 is intended for a temperature range of −40° C. to 85° C., and in a wider temperature range, for example, a temperature range of −40° C. to 125° C., the exterior resin region is cracked by a thermal expansion of the exterior resin as long as the amount of filling in the Document is adopted. More specifically, as the temperature range is wider, the influence of the difference in linear expansion coefficient between the core and the exterior resin is increased to increase the stress generated when the exterior resin is cured or when the coil component is used, and make the exterior resin likely to be cracked.
Patent Document 1: Japanese Patent Application Laid-Open No. 2010-16217